The present invention relates to an ultraviolet/infrared absorbent low transmittance glass. More particularly, it relates to an ultraviolet/infrared absorbent low transmittance glass which has an almost neutral color such as greenish gray shade and which has low visible light transmittance, low solar energy transmittance, and low ultraviolet transmittance, so that it is useful for windows of vehicles or buildings particularly for a privacy protecting glass in a rear window of a vehicle.
Recently, a variety of glasses with ultraviolet/infrared absorptivity to be used as a vehicle windshield have been proposed with the view of preventing degradation of luxurious interior materials and reducing cooling load of the vehicle. In view of privacy protection, glass with relatively low visible light transmittance is preferably used for a rear window glass of a vehicle. Such kinds of glass include the followings.
For example, a dark gray colored infrared absorbent glass disclosed in Japanese Patent H7-29813B consists of soda-lime-silica glass including colorants consisting of 1.00 to 1.7 weight percent Fe2O3 (total iron), at least 0.27 weight percent FeO, 0.002 to 0.005 weight percent Se, and 0.01 to 0.02 weight percent CoO. The glass exhibits luminous transmittance less than 32 percent and total solar infrared transmittance less than 15 percent at 3.9 mm thickness.
A dark gray colored glass disclosed in Japanese Patent H8-157232A consists of soda-lime-silica glass including colorants consisting of 0.8 to 1.4 weight percent Fe2O3 (total iron), less than 0.21 weight percent FeO, 0.05 to 1.0 weight percent TiO2, 0.02 to 0.05 weight percent CoO, and 0.0005 to 0.015 weight percent Se.
A neutral gray colored glass disclosed in claim 25 of U.S. Pat. No. 5,393,593 consists of soda-lime-silica glass including colorants consisting of 1.00 to 2.2 weight percent Fe2O3 (total iron), at least 0.20 weight percent FeO, 0.0005 to 0.005 weight percent Se, and 0.010 to 0.030 weight percent CoO. The glass exhibits luminous transmittance less than 35 percent and total solar infrared transmittance less than 20 percent at 3.9 mm thickness.
A glass disclosed in PCT (Japanese phase) H7-508971 consists of soda-lime-silica glass including colorants consisting of 1.3 to 2.0 weight percent of Fe2O3 (total iron), about 0.01 to 0.05 weight percent of NiO, about 0.02 to 0.04 weight percent of Co3O4, about 0.0002 to 0.003 weight percent of Se and having a ferrous iron value of 18 to 30 weight percent and less than 0.53 of a light and shade coefficient.
In both the dark gray colored infrared absorbent glass disclosed in Japanese Patent H7-29813B and the neutral gray colored glass disclosed in U.S. Pat. No. 5,393,593, a great quantity of Se is used for providing a desirable color. Such a great quantity of Se is unpreferable for the environment because Se has toxicity and is easy to vaporize. The above dark gray glass disclosed in Japanese Patent H8-157232A including 0.05 to 1.0 weight percent TiO2 as an essential component is unpreferable because TiO2 is expensive to increase the batch cost.
The aforementioned glass includes selenium in high concentration to provide optical properties, without essentially including nickel.
The glass disclosed in PCT (Japanese phase) H7-508971 is prepared from standard soda-lime-silica glass to which iron oxide, cobalt oxide, nickel oxide and selenium are added in a specific ratio. However, the glass composition disclosed therein has a great content of selenium and small amount of nickel oxide.
It is an object of the present invention to provide an ultraviolet/infrared absorbent low transmittance glass which has an almost neutral color such as greenish gray and which has low visible light transmittance, low solar energy transmittance and low ultraviolet transmittance so that it is useful for a window of a vehicle or a building particularly for a privacy protecting glass of a rear window of a vehicle.
The ultraviolet/infrared absorbent low transmittance glass of the present invention consists of a base glass, that is, the major constituents comprising:
65 to 80 wt. % SiO2;
0 to 5 wt. % Al2O3;
0 to 10 wt. % MgO;
5 to 15 wt. % CaO wherein a total amount of MgO and CaO is between 5 and 15 wt. %;
10 to 18 wt. % Na2O;
0 to 5 wt. % K2O wherein a total amount of Na2O and K2O is between 10 and 20 wt. %; and
0 to 5 wt. % B2O3, and a colorant including:
1.25 to 1.5 wt. % total iron oxide (Txe2x80x94Fe2O3) expressed as Fe2O3;
0.01 to 0.019 wt. % CoO;
more than 0.0008 wt. % and equal to or less than 0.003 wt. % Se; and
0.055 to 0.1 wt. % NiO.
When it is measured by using C.I.E. standard illuminant xe2x80x9cAxe2x80x9d, the glass with a thickness between 2 and 5 mm has a visible light transmittance (YA) in a range from 10 to 25%, a solar energy transmittance (TG) in a range from 5 to 20% and an ultraviolet transmittance (Tuv) of less than 15%.
In the present invention, the desired color shade can be obtained with a smaller amount of Se, which is desired to be decreased in content because of its toxicity and volatility, and with a greater amount of NiO than the amount conventionally required. It has been understood conventionally that adding nickel to glass is unpreferable because of formation of nickel sulfide stones. However, the formation of nickel sulfide stones is more strongly dependent on the size of nickel grains added in the batch or redox of the glass than the concentration of NiO. When the concentration of NiO in the glass is too high, there is a possibility that NiO coagulates to form the nickel sulfide stones. However, when NiO is in a range defined by this invention, the desired color can be obtained without producing the nickel sulfide stones.
The description will be made as regard to an ultraviolet/infrared absorbent low transmittance glass composition. It should be noted that components will be represented with percentage by weight.
SiO2(silica) is a principal component for forming skeleton of glass. Less than 65% SiO2 lowers the durability of the glass and more than 80% SiO2 raises the melting temperature of the glass so high.
Al2O3 is a component for improving the durability of the glass. More than 5% Al2O3 raises the melting temperature of the glass so high. The preferable range of Al2O3 is between 0.1% and 2%.
MgO and CaO improve the durability of the glass and adjust a devitrification temperature and viscosity of the glass during molding. More than 10% MgO raises the devitrification temperature. Less than 5% or more than 15% CaO raises the devitrification temperature of the glass. The durability of the glass is lowered when the total amount of MgO and CaO is less than 5%, while the devitrification temperature is increased when the total exceeds 15%.
Na2O and K2O prompt the glass to melt. The efficiency of promotion of melting becomes poor when Na2O is less than 10% or the total of Na2O and K2O is less than 10%, while the durability of the glass is lowered when Na2O exceeds 18% or the total of Na2O and K2O exceeds 20%. K2O is preferable not to exceed 5% because of its expensive cost.
B2O3 is a component for improving the durability of the glass, prompting to melt, and yet enhancing the ultraviolet absorption. B2O3 should be less than 5%, since difficulties during molding are caused due to the vaporization of B2O3 when B2O3 exceeds 5%.
Iron oxide is present in the form of Fe2O3 and the form of FeO in the glass. Fe2O3 is a component for improving the ultraviolet absorptivity and FeO is a component for improving the heat rays absorptivity.
When the total amount of iron oxide (Txe2x80x94Fe2O3) expressed as Fe2O3 is less than 1.25%, the efficiency of ultraviolet and infrared absorptivity becomes small so as not to provide desired optical properties. On the other hand, when Txe2x80x94Fe2O3 exceeds 1.5%, there is an unpreferable possibility that the temperature around a crown of a glass melting furnace exceeds its refractory temperature due to absorption of the heat rays by the ferrous oxide. In addition, in case of successively producing glasses by a glass melting furnace with Txe2x80x94Fe2O3 exceeding 1.5%, long time is required to alter a glass composition in the furnace.
More than 1.25% Txe2x80x94Fe2O3 can offer preferably sufficient efficiency of ultraviolet and infrared absorptivity.
Fe2O3 has a function of particularly increasing the absorptivity in ultraviolet range when glass is reinforced by air blast cooling. This means that the glass of this invention can obtain enough efficiency of ultraviolet absorptivity without using expensive ultraviolet absorbent such as CeO2 and TiO2. When Txe2x80x94Fe2O3 is in the range mentioned above, the desired color shade of the glass can be obtained after discoloration due to the reinforcement process by air blast cooling.
When the FeO/Txe2x80x94Fe2O3 ratio (a weight of FeO expressed as Fe2O3 against Txe2x80x94Fe2O3) is too low, the heat rays absorptivity can not be obtained sufficiently because of a small amount of FeO. Many bubbles are also formed in the molten glass because the molten glass is relatively oxidative so that the product yield is lowered. When the FeO/Txe2x80x94Fe2O3 ratio is too high, the visible light transmittance is reduced and the color is of a blue tint. In addition, nickel sulfide stones are sometimes present in the molten glass because the molten glass is relatively reductive. Too high ratio of FeO/Txe2x80x94Fe2O3 is also unpreferable since it causes streaks with enough silica and silica scum.
In the present invention, the FeO/Txe2x80x94Fe2O3 ratio in a range between 0.15 and 0.4 brings a green shade which is an almost neutral color having high ultraviolet absorptivity and high heat rays absorptivity. In this case, values expressed as Fe2O3 are used for the content of FeO.
CoO is a component for forming an almost neutral color such as greenish gray shade by cooperating with Se and/or NiO, and Fe2O3 for controlling the visible light transmittance. Less than 0.01% CoO can not form a desired color shade and makes the visible light transmittance too high. More than 0.019% CoO makes the color too blue tint and reduces the visible light transmittance.
Se contributes a pink color, so that it reduces the excitation purity with the aid of a complementary color of CoO. Less than 0.0008% Se can not form a desired greenish gray shade, and more than 0.003% Se reduces the visible light transmittance. When using Se, the content thereof is preferable in a range between 0.0008% and 0.003%, preferably in a range between 0.001% and 0.0018%.
NiO is a component for controlling the visible light transmittance and reducing the excitation purity as like as CoO. NiO has an absoptivity in a wide infrared range, so that it is a component for reducing the solar energy transmittance as like as FeO. Less then 0.055% NiO can not form a desired color shade. To reduce the solar energy transmittance requires a large amount of FeO which causes difficulties on the production of the glass. When NiO is more than 0.1%, nickel sulfide stones are sometimes present in the product and the visible light transmittance is reduced. In addition, the obtained shade becomes too greenish. When using NiO, the content thereof is preferably in a range between 0.06% and 0.1%.
It is known that the coordination number of NiO varies according to the rate of cooling glass so that the color of the glass varies. This is because the cooling varies the coordination number of oxide around Ni2+ from 6 into 4 and thus varies the optical absorption. The absorption of Ni2+ with octahedral coordination exists around 430 nanometers so as to contribute yellow to the glass, while the absorption of Ni2+ with tetrahedral coordination exists from 500 to 640 nanometers. Therefore, the excitation purity would be reduced to obtain the preferable shade by using Ni2+ with tetrahedral coordination.
A windshield of a passenger car is normally reinforced by air blast cooling for safety. The reinforcement process by air blast cooling improves the absorption of NiO with 4 coordinating atoms, and reduces the visible light transmittance. Although the reinforcement process by air blast cooling reduces the absorption of visible lights, the variations of NiO increases the absorption. The composition of the glass of the present invention is determined such that the optical properties of the glass after the reinforcement process fall in the desired range.
CeO2 is a component for improving the ultraviolet absorptivity and is present in the form of Ce3+ or in the form of Ce4+ in glass. Particularly, Ce3+ is effective in absorbing ultraviolet with less absorptivity in the visible range. In the present invention, oxide of Ce3+ is also expressed in terms of CeO2 and is included in the total amount of CeO2.
TiO2 is a component for improving the ultraviolet absorptivity particularly by interaction with FeO. TiO2 can be added to improve the ultraviolet absorptivity within such a range as not to lose the almost neutral color such as greenish gray shade, or to add a yellow tint in order to obtain the desired color shade. The use of expensive CeO2, TiO2 increases the cost so that it is not preferable to use more than 2% CeO2, TiO2.
One or more than two among MnO, V2O5, MoO3, CuO, Cr2O3, and the like may be added as colorant and SnO2 within a rang from 0% to 1% in total may be added as a reducing agent in such a range as not to lose middle transmittance and the almost neutral color such as greenish gray shade. To further securely prevent the formation of nickel sulfide stones, ZnO may be added in a range from 0% to 1%.
In the present invention, the glass is preferable to be reinforced by the air blasting. The desired color shade and optical properties are obtained in the reinforced process when the glass has the composition of the present invention comprising NiO and Fe2O3 in the specific amount.
In the reinforcement process, the glass plate produced from the molten glass is reheated at 600 to 750xc2x0 C. for 2 to 5 minutes, and then, cooled by blasting air of 10 to 30xc2x0 C. at a cooling rate of 100 to 300xc2x0 C./sec.
The air blasting reinforcement process makes the glass plate comprising NiO and Fe2O3 to have the greenish gray and almost neutral shade, and to have the low visible light transmittance and the low ultraviolet transmittance while keeping the high heat rays absorptivity.
In the present invention, when measured by using C.I.E standard illuminant xe2x80x9cAxe2x80x9d, the glass with a thickness between 2 to 5 mm has a visible light transmittance (YA) in the range from 10% to 25%, a solar energy transmittance (TG) in the range from 5% to 20% and an ultraviolet transmittance (Tuv) defined by ISO of not greater than 15%, preferably not greater than 10%.
In case of using L* a* b* color system, the chromaticity, expressed by a* and b*, of the glass color are preferably in ranges of xe2x88x9210xe2x89xa6a*xe2x89xa60 and xe2x88x923xe2x89xa6b*xe2x89xa67, respectively.
When the glass is used in a rear window of vehicle for the privacy protection, since almost neutral colored glass is particularly preferred, the chromaticity is in the ranges of xe2x88x925xe2x89xa6a *xe2x89xa60 and 0xe2x89xa6b*xe2x89xa65.
When measured by using C.I.E. standard illuminant xe2x80x9cCxe2x80x9d over the wavelength range from 380 to 770 nanometers, the glass of the present invention preferably has optical properties with a dominant wavelength (xcexd) in the range from 480 to 580 nanometers and an excitation purity (Pe) of less than 10%.